We report on an investigation of the lattice dynamical properties in a range of Fe1+yTe1−xSex compounds, with special emphasis on the c-axis polarized vibration of Fe with B1g symmetry, a Raman active mode common to all families of Fe-based superconductors. We have carried out a systematic study of the temperature dependence of this phonon mode as a function of Se x and excess Fe y concentrations. In parent compound Fe1+yTe, we observe an unconventional broadening of the phonon between room temperature and magnetic ordering temperature TN . The situation smoothly evolves toward a regular anharmonic behavior as Te is substituted for Se and long range magnetic order is replaced by superconductivity. Irrespective to Se contents, excess Fe is shown to provide an additional damping channel for the B1g phonon at low temperatures. We performed Density Functional Theory ab initio calculations within the local density approximation to calculate the phonon frequencies including magnetic polarization and Fe non-stoichiometry in the virtual crystal approximation. We obtained a good agreement with the measured phonon frequencies in the Fe-deficient samples, while the effects of Fe excess are poorly reproduced. This may be due to excess Fe-induced local magnetism and low energy magnetic fluctuations that can not be treated accurately within these approaches. As recently revealed by neutron scattering and muon spin rotation studies, these phenomena occur in the temperature range where anomalous decay of the B1g phonon is observed and suggests a peculiar coupling of this mode with local moments and spin fluctuations in Fe1+yTe1−xSex.

We report an investigation of the lattice dynamical properties of LiFeAs using inelastic light scattering. Five of the six expected phonon modes are observed. The temperature evolution of their frequencies and linewidths is in good agreement with an anharmonic-decay model. We find no evidence for substantial electron-phonon coupling, and no superconductivity-induced phonon anomalies.

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We report a systematic investigation of band-edge photoluminescence of the diluted magnetic semiconductor alloy Zn 1−x Mn x Se for a series of compositions (0 < x < 0.485). The specimens investigated were in the form of thin films fabricated by molecular beam epitaxy. The near band-edge emissions of donor-bound excitons (designated as I 2 ) and of neutral acceptor-bound excitons (I 1 ) were systematically investigated as a function of temperature and of alloy composition. These measurements also allowed us to determine the LO-phonon energy hω LO = 31.2 ± 0.2 meV. From the temperature dependence of the bound exciton peak, the Varshni temperature parameter α was found to increase linearly with increasing Mn concentration x, while β decreased with x. From the temperature dependence of the full width at half maximum (FWHM) of the I 2 emission line, the broadening factors (T ) were determined from the fit to the data. For x > 0.20 the effect of inhomogeneous broadening inh on (T ) was found to be stronger than that of the longitudinal optical phonon term LO . Furthermore, the activation energies of thermal quenching were obtained for both the I 2 and the I 1 peaks from the temperature dependence of the bound exciton peaks, and were found to decrease with increasing Mn concentration. Finally, we show that at high temperature the broadening of the FWHM is dominated by the LO-phonon interaction.

Quantum point contact (QPC) with an extra metallic gate in between the split gates of a conventional QPC was fabricated and studied. Clear conductance quantization was observed at 4.2 K when a proper positive voltage was set to the middle gate of the QPC. The maximum energy spacing between the ground and the first exited state of the QPC was around 7 meV which is at least a few times larger than that of conventional QPCs. Using same approach, a possibility of making a relatively clean and long 1D wire has been tested.